To what degree juvenile migrant birds are able to correct for orientation errors
or wind drift is still largely unknown. We studied the orientation of passerines
on the Faroe Islands far off the normal migration routes of European migrants.
The ability to compensate for displacement was tested in naturally occurring
vagrants presumably displaced by wind and in birds experimentally displaced 1100
km from Denmark to the Faroes. The orientation was studied in orientation cages
as well as in the free-flying birds after release by tracking departures using
small radio transmitters. Both the naturally displaced and the experimentally
displaced birds oriented in more easterly directions on the Faroes than was
observed in Denmark prior to displacement. This pattern was even more pronounced
in departure directions, perhaps because of wind influence. The clear
directional compensation found even in experimentally displaced birds indicates
that first-year birds can also possess the ability to correct for displacement
in some circumstances, possibly involving either some primitive form of true
navigation, or ‘sign posts’, but the cues used for this are highly
speculative. We also found some indications of differences between species in
the reaction to displacement. Such differences might be involved in the
diversity of results reported in displacement studies so far.
We present data suggesting that Northern Wheatears (Oenanthe oenanthe leucorhoa) breeding in West Greenland and Canada may be able to accomplish migration to their wintering grounds in West Africa in one direct, transatlantic crossing of more than 4000 km (great circle distance). This conclusion is based on analyses of wing lengths, body weights, and timing of departure from West Greenland and arrival on an island 350 km off the coast of Morocco. Previously, it has been suggested that Nearctic wheatears migrate to Africa by a two-step journey, the first leg comprising a shorter transatlantic crossing to western Europe. A long, direct flight has previously been considered unfeasible as the predicted flight costs were considered to be too high. However, recent insights in aerodynamic theory make these long ocean crossings appear more feasible, especially when taking the use of tailwinds into account.
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